HELP!!

I've tried going over the stop with positive reinforcement, I've tried behavior charts, time outs, losing privileges, losing toys/screentime, even spanking...which I never wanted to do but what else is there?? My daughter will NOT stop hitting and pushing her 2 year old brother. She's not doing it for attention because she does it when I'm not looking or waits til I'm out of the room. It is completely unprovoked and seemingly out of nowhere. Any tricks to stopping this behavior?? It's to the point where I really can't leave her alone with him..I'm afraid he's going to get seriously hurt if he's shoved and falls into or onto something. 😔